Why it won't work
Martial arts are highly skill-oriented and require significant feedback from an instructor, as well as copious amounts of sparring (either with striking, such as boxing and Muay Thai, or with wrestling, such as judo, Brazilian jiu-jitsu or wrestling). "Learning" a martial art without those two key components is almost always a fruitless endeavor.
There are scenarios where people already skilled in one combat sport are able to successfully learn techniques from another, similar art. A commonly used example is mixed martial arts fighter Evan Tanner, who taught himself Brazilian jiu-jitsu submissions from the tapes produced by Rorion Gracie. Tanner succeeded in large part because he had a background in wrestling and he was able to practice the moves with resisting partners at home.
Trying to learn techniques at home, without an instructor, without sparring partners, and with training material of unknown quality, is a tough path even for people with some amount of training under their belts. It's unlikely that you'll be very productive starting as an untrained person.
What to do instead
It would be better to spend your time becoming strong, fast and fit. Lifting, improving mobility, running and doing metabolic conditioning like hill sprints or pushing a Prowler are all very effective ways to improve your physicality while you raise the cash necessary to join a boxing gym.
You can also look into some sort of work-study program at the local training centers. Some gyms will let you train for reduced prices or even free if you spend a couple hours cleaning up the practice space after class.